Ceramic or refractory materials, such as bricks, tiles and the like, are cured by firing in a furnace known as a kiln. For example, bricks may be cured by firing in a roof-fired ceramic kiln. Stacks of bricks are placed on wheeled pallets that are known as kiln cars. The kiln cars are moved slowly through the kiln from one end to the other. The kiln has a preheating zone at one end, a cooling zone at the opposite end, and a heating zone in between. Burners and/or injectors at the roof of the kiln cause flames to project downward into the heating zone to heat the bricks as they move through the kiln.
Typically, the stacks of bricks are spaced apart from each other and are indexed through the kiln. The flames are projected downward into the spaces between the stacks of bricks for a period of time. The kiln cars are then advanced forward to their next positions, and the flames are again projected downward into the spaces between the stacks of bricks. This process repeats until all of the stacks of bricks have been moved sequentially through the preheating zone, the heating zone, and the cooling zone to emerge from the kiln in a heat-treated state.
The burners and injectors in a roof-fired kiln can be arranged in long rows above a wide area. However, projecting the flames downward from above can cause the stacks of bricks to become heated more quickly near the top than the bottom.